Our work addresses this problem in the domain of water management at a catchment scale and consists in evaluating water balances. We have developed a software framework allowing simulation scenarios to be easily run and results about outlet flow and groundwater variation to be easily interpreted. In this paper, we study anthropogenic scenarios consisting in modifying the land cover at different scales: parcel, slopes or catchment. The simulation is supported by a methodology allowing catchment models to be built up using a hierarchical and modular approach based on components formalised by sequential machines. Few modelling parameters are necessary because our purpose is not to build up a "perfect" model to represent a catchment from a hydrological point of view but to illustrate the impact of climatic changes or anthropogenic activities on water balance. The simulation interface allows climatic data files to be selected to compare various scenarios. It allows the land-use to be easily modified to understand the impact of anthropogenic activities on water from a quantitative point of view. Modelling and results of simulation are illustrated on a catchment located in the area of Cévennes (South of France).